1. Field of the Invention
The present invention concerns a system for cooling a gas turbine by bleeding air from the compressor.
2. Description of the Prior Art
In engines cooled by air from the interior of the high-pressure rotor, the cooling air is bled from the jet stream through ports made in the collars of the compressor drum.
These openings have the drawback of limiting the maximum permissible size of the collar's radius. Indeed, the collar is strongly acted upon by centrifugal force; if openings are made in it, in order to obtain the desired passage section, it is often necessary to increase the distance between two discs and therefore the length of the brace. This increase in the length of the brace, added to the effect of the shape coefficient due to the holes, raises the level of local stresses, in particular bending stresses, thus the necessity of reducing the diameter of the brace collars.
This restriction on the diameter of the collars leads to consequences in the technology of the elements in the jet stream and for the cooling output. With regard to the technology of the jet stream elements, this restriction on the diameter of the collars makes it impossible to make prismatic connections which are less costly than broached connections. Prismatic connections in fact induce high bending stresses on the disc, and in order to bring these stresses down to an acceptable level it is recommended that the brace collars be placed as high as possible towards the rim. As previously discussed, this arrangement is incompatible with the presence of cooling holes, which also generate major bending stresses. With regard to cooling, the size of the dead space leads to recirculations that perturb the cooling-air flow.
In order to give the air flow a certain minimum efficiency, it is necessary to accelerate the flow by means of centripetal gills or tubes.